1. Field of the Invention
The invention relates generally to apparatus and methods for identifying gases within formation fluids obtained from a subterranean formation. More particularly, the invention relates to apparatus and methods for identifying and quantifying the amount of acid gases such as hydrogen sulfide (H2S) and carbon dioxide (CO2) in such formation fluids.
2. Background of the Technology
Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, i.e., a reservoir, by drilling a wellbore that penetrates the reservoir. Once a wellbore has been drilled, the well must be completed before hydrocarbons can be produced from the well. A well completion involves the design, selection, and installation of equipment and materials in or around the wellbore for conveying, pumping, and/or controlling the production or injection of fluids. After the well has been completed, production of oil and gas can begin.
In the construction of hydrocarbon production, processing and transportation facilities, it is often desirable to know the type and concentration of gases contained within the formation fluids in order to select the appropriate materials for the design of wellbore facilities. For example, it is advantageous to know whether corrosive materials, such as acid gases like hydrogen sulfide (H2S) and carbon dioxide (CO2), are contained within the formation fluids since an underestimate of such gases can impact well economics and lead to premature equipment and piping failures. This is particularly true with H2S gas since it is highly corrosive and toxic. Further, more recently it has been observed that the proportion of H2S within formation fluids is increasing, as a result of accessing deeper and more technically challenging formations and where the hydrocarbon deposits tend to be of lesser quality.
Conventionally, downhole formation fluid samples are taken for chemical and physical analysis. Such samples of formation fluid, also known as reservoir fluid, are typically collected as early as possible in the life of a reservoir for analysis at the surface and, more particularly, in specialized laboratories. The information that such analysis provides is vital in the planning and development of hydrocarbon reservoirs, as well as in the assessment of a reservoir's capacity and performance. However, when analyzing such samples later on the surface, those in the art recognize that the measured values may not be representative of the actual values in that some of the formation fluids (e.g., H2S gas) may react with metals used in downhole tools to obtain such samples. In addition, residual amounts of drilling fluids left in the wellbore or near wellbore area of the formation often contain chemical agents that comingle with the sampled formation fluids acquired with conventional tools. This may be particularly problematic with H2S gas because drilling fluids typically contain chemicals that scavenge and neutralize such acid gases. Moreover, in some wells it may not be possible to use some conventional fluid sampling tools due to very high pressures and temperatures, especially in those wells currently being drilled to extreme depths in the Gulf of Mexico.
Accordingly, there remains a need in the art for apparatus and methods for identifying the presence and concentration of certain gases in hydrocarbon formation fluids. Such apparatus and methods would be particularly well-received if they offered the potential to obviate or mitigate at least one or more of the aspects associated with the aforementioned disadvantages.